Accessing multiple virtual devices

ABSTRACT

In one aspect, a method includes receiving a first I/O at a kernel interface using a pseudo data storage system, writing the first I/O to a first virtual device on a datastore, receiving a second I/O at the kernel interface using the pseudo data storage system and writing the second I/O to a second virtual device on the datastore.

BACKGROUND

Computer data is vital to today's organizations and a significant part of protection against disasters is focused on data protection. As solid-state memory has advanced to the point where cost of memory has become a relatively insignificant factor, organizations can afford to operate with systems that store and process terabytes of data.

Conventional data protection systems include tape backup drives, for storing organizational production site data on a periodic basis. Another conventional data protection system uses data replication, by creating a copy of production site data of an organization on a secondary backup storage system, and updating the backup with changes. The backup storage system may be situated in the same physical location as the production storage system, or in a physically remote location. Data replication systems generally operate either at the application level, at the file system level, or at the data block level.

SUMMARY

In one aspect, a method includes receiving a first I/O at a kernel interface using a pseudo data storage system, writing the first I/O to a first virtual device on a datastore, receiving a second I/O at the kernel interface using the pseudo data storage system and writing the second I/O to a second virtual device on the datastore.

In another aspect, an apparatus includes electronic hardware circuitry configured to receive a first I/O at a kernel interface using a pseudo data storage system, write the first I/O to a first virtual device on a datastore, receive a second I/O at the kernel interface using the pseudo data storage system and write the second I/O to a second virtual device on the datastore.

In a further aspect, an article includes a non-transitory computer-readable medium that stores computer-executable instructions. The instructions cause a machine to receive a first I/O at a kernel interface using a pseudo data storage system, write the first I/O to a first virtual device on a datastore, receive a second I/O at the kernel interface using the pseudo data storage system and write the second I/O to a second virtual device on the datastore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a data protection system.

FIG. 2 is an illustration of an example of a journal history of write transactions for a storage system.

FIG. 3 is a block diagram of an example of the data protection system used in a virtual environment.

FIG. 4A is a simplified block diagram of an example of a data replication system in a virtual environment with splitters at a kernel.

FIG. 4B is a simplified block diagram of an example of a data replication system of FIG. 4A that includes a shadow virtual machine.

FIG. 5 is a flowchart of an example of a process to generate a shadow virtual machine.

FIG. 6 is a flowchart of an example of a process to perform a target side write.

FIG. 7 is a flowchart of an example of a process to perform a target side read.

FIG. 8 is a simplified block diagram of an example of a data replication system of FIG. 4A that includes a pseudo device.

FIG. 9 is a flowchart of an example of a process to access a journal on a virtual device using the pseudo device.

FIG. 10 is a simplified block diagram of an example of a computer on which any of the process of FIGS. 5 to 7 and 9 may be implemented.

DETAILED DESCRIPTION

Described herein is a replication system that allows reading and writing of data to multiple virtual disks via a single pseudo data storage system (or a smaller number of pseudo data storage systems). The pseudo data storage system is used to access journals and repository volumes in a virtual environment.

The following definitions may be useful in understanding the specification and claims.

BACKUP SITE—a facility where replicated production site data is stored; the backup site may be located in a remote site or at the same location as the production site;

BOOKMARK—a bookmark is metadata information stored in a replication journal which indicates a point in time.

DATA PROTECTION APPLIANCE (DPA)—a computer or a cluster of computers responsible for data protection services including inter alia data replication of a storage system, and journaling of I/O requests issued by a host computer to the storage system;

HOST—at least one computer or networks of computers that runs at least one data processing application that issues I/O requests to one or more storage systems; a host is an initiator with a SAN;

HOST DEVICE—an internal interface in a host, to a logical storage unit;

IMAGE—a copy of a logical storage unit at a specific point in time;

INITIATOR—a node in a SAN that issues I/O requests;

I/O REQUEST—an input/output request (sometimes referred to as an I/O), which may be a read I/O request (sometimes referred to as a read request or a read) or a write I/O request (sometimes referred to as a write request or a write);

JOURNAL—a record of write transactions issued to a storage system; used to maintain a duplicate storage system, and to roll back the duplicate storage system to a previous point in time;

LOGICAL UNIT—a logical entity provided by a storage system for accessing data from the storage system. The logical disk may be a physical logical unit or a virtual logical unit;

LUN—a logical unit number for identifying a logical unit;

PHYSICAL LOGICAL UNIT—a physical entity, such as a disk or an array of disks, for storing data in storage locations that can be accessed by address;

PRODUCTION SITE—a facility where one or more host computers run data processing applications that write data to a storage system and read data from the storage system;

REMOTE ACKNOWLEDGEMENTS—an acknowledgement from remote DPA to the local DPA that data arrived at the remote DPA (either to the appliance or the journal)

SPLITTER ACKNOWLEDGEMENT—an acknowledgement from a DPA to the protection agent (splitter) that data has been received at the DPA; this may be achieved by an SCSI status command.

SAN—a storage area network of nodes that send and receive an I/O and other requests, each node in the network being an initiator or a target, or both an initiator and a target;

SOURCE SIDE—a transmitter of data within a data replication workflow, during normal operation a production site is the source side; and during data recovery a backup site is the source side, sometimes called a primary side;

STORAGE SYSTEM—a SAN entity that provides multiple logical units for access by multiple SAN initiators

TARGET—a node in a SAN that replies to I/O requests;

TARGET SIDE—a receiver of data within a data replication workflow; during normal operation a back site is the target side, and during data recovery a production site is the target side, sometimes called a secondary side;

THIN PROVISIONING—thin provisioning involves the allocation of physical storage when it is needed rather than allocating the entire physical storage in the beginning. Thus, use of thin provisioning is known to improve storage utilization.

THIN LOGICAL UNIT—a thin logical unit is a logical unit that uses thin provisioning;

VIRTUAL LOGICAL UNIT—a virtual storage entity which is treated as a logical unit by virtual machines;

WAN—a wide area network that connects local networks and enables them to communicate with one another, such as the Internet.

A description of journaling and some techniques associated with journaling may be described in the patent titled “METHODS AND APPARATUS FOR OPTIMAL JOURNALING FOR CONTINUOUS DATA REPLICATION” and with U.S. Pat. No. 7,516,287, which is hereby incorporated by reference.

Referring to FIG. 1, a data protection system 100 includes two sites; Site I, which is a production site, and Site II, which is a backup site or replica site. Under normal operation the production site is the source side of system 100, and the backup site is the target side of the system. The backup site is responsible for replicating production site data. Additionally, the backup site enables roll back of Site I data to an earlier pointing time, which may be used in the event of data corruption of a disaster, or alternatively in order to view or to access data from an earlier point in time.

FIG. 1 is an overview of a system for data replication of either physical or virtual logical units. Thus, one of ordinary skill in the art would appreciate that in a virtual environment a hypervisor, in one example, would consume logical units and generate a distributed file system on them such as VMFS creates files in the file system and expose the files as logical units to the virtual machines (each VMDK (Virtual Machine Disk) is seen as a SCSI device by virtual hosts). In another example, the hypervisor consumes a network based file system and exposes files in the NFS as SCSI devices to virtual hosts.

During normal operations, the direction of replicate data flow goes from source side to target side. It is possible, however, for a user to reverse the direction of replicate data flow, in which case Site I starts to behave as a target backup site, and Site II starts to behave as a source production site. Such change of replication direction is referred to as a “failover”. A failover may be performed in the event of a disaster at the production site, or for other reasons. In some data architectures, Site I or Site II behaves as a production site for a portion of stored data, and behaves simultaneously as a backup site for another portion of stored data. In some data architectures, a portion of stored data is replicated to a backup site, and another portion is not.

The production site and the backup site may be remote from one another, or they may both be situated at a common site, local to one another. Local data protection has the advantage of minimizing data lag between target and source, and remote data protection has the advantage is being robust in the event that a disaster occurs at the source side.

The source and target sides communicate via a wide area network (WAN) 128, although other types of networks may be used.

Each side of system 100 includes three major components coupled via a storage area network (SAN); namely, (i) a storage system, (ii) a host computer, and (iii) a data protection appliance (DPA). Specifically with reference to FIG. 1, the source side SAN includes a source host computer 104, a source storage system 108, and a source DPA 112. Similarly, the target side SAN includes a target host computer 116, a target storage system 120, and a target DPA 124. As well, the protection agent (sometimes referred to as a splitter) may run on the host, or on the storage, or in the network or at a hypervisor level, and that DPAs are optional and DPA code may run on the storage array too, or the DPA 124 may run as a virtual machine.

Generally, a SAN includes one or more devices, referred to as “nodes”. A node in a SAN may be an “initiator” or a “target”, or both. An initiator node is a device that is able to initiate requests to one or more other devices; and a target node is a device that is able to reply to requests, such as SCSI commands, sent by an initiator node. A SAN may also include network switches, such as fiber channel switches. The communication links between each host computer and its corresponding storage system may be any appropriate medium suitable for data transfer, such as fiber communication channel links.

The host communicates with its corresponding storage system using small computer system interface (SCSI) commands.

System 100 includes source storage system 108 and target storage system 120. Each storage system includes physical storage units for storing data, such as disks or arrays of disks. Typically, storage systems 108 and 120 are target nodes. In order to enable initiators to send requests to storage system 108, storage system 108 exposes one or more logical units (LU) to which commands are issued. Thus, storage systems 108 and 120 are SAN entities that provide multiple logical units for access by multiple SAN initiators.

Logical units are a logical entity provided by a storage system, for accessing data stored in the storage system. The logical unit may be a physical logical unit or a virtual logical unit. A logical unit is identified by a unique logical unit number (LUN). Storage system 108 exposes a logical unit 136, designated as LU A, and storage system 120 exposes a logical unit 156, designated as LU B.

LU B is used for replicating LU A. As such, LU B is generated as a copy of LU A. In one embodiment, LU B is configured so that its size is identical to the size of LU A. Thus, for LU A, storage system 120 serves as a backup for source side storage system 108. Alternatively, as mentioned hereinabove, some logical units of storage system 120 may be used to back up logical units of storage system 108, and other logical units of storage system 120 may be used for other purposes. Moreover, there is symmetric replication whereby some logical units of storage system 108 are used for replicating logical units of storage system 120, and other logical units of storage system 120 are used for replicating other logical units of storage system 108.

System 100 includes a source side host computer 104 and a target side host computer 116. A host computer may be one computer, or a plurality of computers, or a network of distributed computers, each computer may include inter alia a conventional CPU, volatile and non-volatile memory, a data bus, an I/O interface, a display interface and a network interface. Generally a host computer runs at least one data processing application, such as a database application and an e-mail server.

Generally, an operating system of a host computer creates a host device for each logical unit exposed by a storage system in the host computer SAN. A host device is a logical entity in a host computer, through which a host computer may access a logical unit. Host device 104 identifies LU A and generates a corresponding host device 140, designated as Device A, through which it can access LU A. Similarly, host computer 116 identifies LU B and generates a corresponding device 160, designated as Device B.

In the course of continuous operation, host computer 104 is a SAN initiator that issues I/O requests (write/read operations) through host device 140 to LU A using, for example, SCSI commands. Such requests are generally transmitted to LU A with an address that includes a specific device identifier, an offset within the device, and a data size. Offsets are generally aligned to 512 byte blocks. The average size of a write operation issued by host computer 104 may be, for example, 10 kilobytes (KB); i.e., 20 blocks. For an I/O rate of 50 megabytes (MB) per second, this corresponds to approximately 5,000 write transactions per second.

System 100 includes two data protection appliances, a source side DPA 112 and a target side DPA 124. A DPA performs various data protection services, such as data replication of a storage system, and journaling of I/O requests issued by a host computer to source side storage system data. As explained in detail herein, when acting as a target side DPA, a DPA may also enable roll back of data to an earlier point in time, and processing of rolled back data at the target site. Each DPA 112 and 124 is a computer that includes inter alia one or more conventional CPUs and internal memory.

For additional safety precaution, each DPA is a cluster of such computers. Use of a cluster ensures that if a DPA computer is down, then the DPA functionality switches over to another computer. The DPA computers within a DPA cluster communicate with one another using at least one communication link suitable for data transfer via fiber channel or IP based protocols, or such other transfer protocol. One computer from the DPA cluster serves as the DPA leader. The DPA cluster leader coordinates between the computers in the cluster, and may also perform other tasks that require coordination between the computers, such as load balancing.

In the architecture illustrated in FIG. 1, DPA 112 and DPA 124 are standalone devices integrated within a SAN. Alternatively, each of DPA 112 and DPA 124 may be integrated into storage system 108 and storage system 120, respectively, or integrated into host computer 104 and host computer 116, respectively. Both DPAs communicate with their respective host computers through communication lines such as fiber channels using, for example, SCSI commands or any other protocol.

DPAs 112 and 124 are configured to act as initiators in the SAN; i.e., they can issue I/O requests using, for example, SCSI commands, to access logical units on their respective storage systems. DPA 112 and DPA 124 are also configured with the necessary functionality to act as targets; i.e., to reply to I/O requests, such as SCSI commands, issued by other initiators in the SAN, including inter alia their respective host computers 104 and 116. Being target nodes, DPA 112 and DPA 124 may dynamically expose or remove one or more logical units.

As described hereinabove, Site I and Site II may each behave simultaneously as a production site and a backup site for different logical units. As such, DPA 112 and DPA 124 may each behave as a source DPA for some logical units, and as a target DPA for other logical units, at the same time.

Host computer 104 and host computer 116 include protection agents 144 and 164, respectively. Protection agents 144 and 164 intercept SCSI commands issued by their respective host computers, via host devices to logical units that are accessible to the host computers. A data protection agent may act on an intercepted SCSI commands issued to a logical unit, in one of the following ways: send the SCSI commands to its intended logical unit; redirect the SCSI command to another logical unit; split the SCSI command by sending it first to the respective DPA; after the DPA returns an acknowledgement, send the SCSI command to its intended logical unit; fail a SCSI command by returning an error return code; and delay a SCSI command by not returning an acknowledgement to the respective host computer.

A protection agent may handle different SCSI commands, differently, according to the type of the command. For example, a SCSI command inquiring about the size of a certain logical unit may be sent directly to that logical unit, while a SCSI write command may be split and sent first to a DPA associated with the agent. A protection agent may also change its behavior for handling SCSI commands, for example as a result of an instruction received from the DPA.

Specifically, the behavior of a protection agent for a certain host device generally corresponds to the behavior of its associated DPA with respect to the logical unit of the host device. When a DPA behaves as a source site DPA for a certain logical unit, then during normal course of operation, the associated protection agent splits I/O requests issued by a host computer to the host device corresponding to that logical unit. Similarly, when a DPA behaves as a target device for a certain logical unit, then during normal course of operation, the associated protection agent fails I/O requests issued by host computer to the host device corresponding to that logical unit.

Communication between protection agents and their respective DPAs may use any protocol suitable for data transfer within a SAN, such as fiber channel, or SCSI over fiber channel. The communication may be direct, or via a logical unit exposed by the DPA. Protection agents communicate with their respective DPAs by sending SCSI commands over fiber channel.

Protection agents 144 and 164 are drivers located in their respective host computers 104 and 116. Alternatively, a protection agent may also be located in a fiber channel switch, or in any other device situated in a data path between a host computer and a storage system or on the storage system itself. In a virtualized environment, the protection agent may run at the hypervisor layer or in a virtual machine providing a virtualization layer.

What follows is a detailed description of system behavior under normal production mode, and under recovery mode.

In production mode DPA 112 acts as a source site DPA for LU A. Thus, protection agent 144 is configured to act as a source side protection agent; i.e., as a splitter for host device A. Specifically, protection agent 144 replicates SCSI I/O write requests. A replicated SCSI I/O write request is sent to DPA 112. After receiving an acknowledgement from DPA 124, protection agent 144 then sends the SCSI I/O write request to LU A. After receiving a second acknowledgement from storage system 108 host computer 104 acknowledges that an I/O command complete.

When DPA 112 receives a replicated SCSI write request from data protection agent 144, DPA 112 transmits certain I/O information characterizing the write request, packaged as a “write transaction”, over WAN 128 to DPA 124 on the target side, for journaling and for incorporation within target storage system 120.

DPA 112 may send its write transactions to DPA 124 using a variety of modes of transmission, including inter alia (i) a synchronous mode, (ii) an asynchronous mode, and (iii) a snapshot mode. In synchronous mode, DPA 112 sends each write transaction to DPA 124, receives back an acknowledgement from DPA 124, and in turns sends an acknowledgement back to protection agent 144. Protection agent 144 waits until receipt of such acknowledgement before sending the SCSI write request to LU A.

In asynchronous mode, DPA 112 sends an acknowledgement to protection agent 144 upon receipt of each I/O request, before receiving an acknowledgement back from DPA 124.

In snapshot mode, DPA 112 receives several I/O requests and combines them into an aggregate “snapshot” of all write activity performed in the multiple I/O requests, and sends the snapshot to DPA 124, for journaling and for incorporation in target storage system 120. In snapshot mode DPA 112 also sends an acknowledgement to protection agent 144 upon receipt of each I/O request, before receiving an acknowledgement back from DPA 124.

For the sake of clarity, the ensuing discussion assumes that information is transmitted at write-by-write granularity.

While in production mode, DPA 124 receives replicated data of LU A from DPA 112, and performs journaling and writing to storage system 120. When applying write operations to storage system 120, DPA 124 acts as an initiator, and sends SCSI commands to LU B.

During a recovery mode, DPA 124 undoes the write transactions in the journal, so as to restore storage system 120 to the state it was at, at an earlier time.

As described hereinabove, LU B is used as a backup of LU A. As such, during normal production mode, while data written to LU A by host computer 104 is replicated from LU A to LU B, host computer 116 should not be sending I/O requests to LU B. To prevent such I/O requests from being sent, protection agent 164 acts as a target site protection agent for host Device B and fails I/O requests sent from host computer 116 to LU B through host Device B.

Target storage system 120 exposes a logical unit 176, referred to as a “journal LU”, for maintaining a history of write transactions made to LU B, referred to as a “journal”. Alternatively, journal LU 176 may be striped over several logical units, or may reside within all of or a portion of another logical unit. DPA 124 includes a journal processor 180 for managing the journal.

Journal processor 180 functions generally to manage the journal entries of LU B. Specifically, journal processor 180 enters write transactions received by DPA 124 from DPA 112 into the journal, by writing them into the journal LU, reads the undo information for the transaction from LU B. updates the journal entries in the journal LU with undo information, applies the journal transactions to LU B, and removes already-applied transactions from the journal.

Referring to FIG. 2, which is an illustration of a write transaction 200 for a journal. The journal may be used to provide an adaptor for access to storage 120 at the state it was in at any specified point in time. Since the journal contains the “undo” information necessary to roll back storage system 120, data that was stored in specific memory locations at the specified point in time may be obtained by undoing write transactions that occurred subsequent to such point in time.

Write transaction 200 generally includes the following fields: one or more identifiers; a time stamp, which is the date & time at which the transaction was received by source side DPA 112; a write size, which is the size of the data block; a location in journal LU 176 where the data is entered; a location in LU B where the data is to be written; and the data itself.

Write transaction 200 is transmitted from source side DPA 112 to target side DPA 124. As shown in FIG. 2, DPA 124 records the write transaction 200 in the journal that includes four streams. A first stream, referred to as a DO stream, includes new data for writing in LU B. A second stream, referred to as an DO METADATA stream, includes metadata for the write transaction, such as an identifier, a date & time, a write size, a beginning address in LU B for writing the new data in, and a pointer to the offset in the DO stream where the corresponding data is located. Similarly, a third stream, referred to as an UNDO stream, includes old data that was overwritten in LU B; and a fourth stream, referred to as an UNDO METADATA, include an identifier, a date & time, a write size, a beginning address in LU B where data was to be overwritten, and a pointer to the offset in the UNDO stream where the corresponding old data is located.

In practice each of the four streams holds a plurality of write transaction data. As write transactions are received dynamically by target DPA 124, they are recorded at the end of the DO stream and the end of the DO METADATA stream, prior to committing the transaction. During transaction application, when the various write transactions are applied to LU B, prior to writing the new DO data into addresses within the storage system, the older data currently located in such addresses is recorded into the UNDO stream. In some examples, the metadata stream (e.g., UNDO METADATA stream or the DO METADATA stream) and the data stream (e.g., UNDO stream or DO stream) may be kept in a single stream each (i.e., one UNDO data and UNDO METADATA stream and one DO data and DO METADATA stream) by interleaving the metadata into the data stream.

Referring to FIG. 3, an example of the data protection system used in a virtual environment is a data protection system 300. The system 300 includes virtual machine hosts (hypervisors) (e.g., a virtual machine hosts (hypervisors) 302 a-302 c), storage arrays (a storage array 306 a, 306 b) and a wide area network (WAN) 304. The virtual machine hosts (hypervisors) 302 a, 302 b and the storage array 306 a are on the productions site and the virtual machine hosts (hypervisors) 302 c and the storage array 306 b are on the replication site. In one example, the virtual machine monitors 302 a-302 c is a MICROSOFT® HYPER-V®. In another example, the virtual machine monitors 302 a-302 c is a VMWARE® virtualization.

The virtual machine monitor 302 a includes virtual machines (e.g., virtual machines 308 a, 308 b), a splitter 314 a and virtual machine hard drive (VHD) (e.g., VHD 316 a) and the virtual machine hosts (hypervisors) 302 b includes a virtual data protection appliance (DPA) 312 a, virtual machines (e.g., virtual machines 308 c, 308 d), a splitter 314 a, VHDs (e.g., VHD 316 b) and a journal virtual disk 320 a. The VHDs 316 a, 316 b and the journal 320 a are part of a file system 310 a. The splitters 314 a, 314 b intercept I/Os arriving to the virtual hard drives, VHDs 316 a, 316 b, respectively. In one example, the file system 310 a is a clustered shared volume file system (Microsoft® CSVFS) or a VMWARE® file system (VMFS). In another example the virtual disks are VMWARE® VVOLS or virtual volumes.

The virtual machine host (hypervisor) 302 c includes a data protection appliance 312 a, a splitter 314 a, a virtual disk 316 c and a journal 320 b. The VHD 316 c and the journal 320 b are part of a file system 310 b. In one example, the file system 310 a is a CSVFS or a VMFS. In one example, the journals 320 a, 320 b are each VHDs.

In one example, an I/O from a VM 308 a that is directed to a virtual disk 316 a is split by the splitter 314 a to the DPA 312 b (via the DPA 312 a and the WAN 304) recorded by the journal 320 b to be stored on the virtual disk 316 c.

Referring to FIG. 4A, a replication system 400 includes splitters at a kernel. In particular, the replication system 400 includes virtual machine hosts 412 a-412 c and datastores 420 a-420 c. The virtual machine host 412 a includes a source virtual data protection appliance (vDPA) 408 a, a source virtual machine (VM) 410 a, a source splitter 414 a at a kernel. The virtual machine host 412 b includes a target vDPA 408 b. The virtual machine host 412 c includes a target splitter 414 b at a kernel and a target VM 410 b. The datastore 420 a includes a source VMDK 416 a, the datastore 420 b includes a replica journal 418 and the datastore 420 c includes a target VMDK 416 c.

The source splitter 414 a sends I/Os from the source VM 410 a to the source VMDK 416 a and to the source vDPA 408 a, which send the I/Os to target vDPA 408 b to be recorded in the replica journal 418 (similar to the processes described for FIGS. 1 and 2).

In one example, the vDPA 408 a can perform a production read using the source splitter 414 a. The source splitter 414 a can poll the vDPA 408 a, receive metadata of I/Os, read from the source VMDK 416 a and write to the vDPA 408 a

However, the vDPA 408 b is unable to access efficiently the target VMDK 416 b. In particular, there is no interface to the target VMDK 416 b that provides efficient and scalable access to the target VMDK 416 b. For example, VMDKs can be accessed efficiently only if VMs use them (i.e., the target VMDK cannot be accessed efficiently if there is no VM attached to it and opening the disk) and a VM can only have up to 60 VMDKs attached to it.

If a VM with VMDK 416 b is powered up, the kernel splitter 414 b is able to access the VMDK 416 b as an I/O stack is generated when a process (e.g., a user process) opens the target VMDK 416 b. To facilitate this the replication system 400 maintains a powered-up target VM 410 b with the target VMDK 416 b attached to it. Using the target VM 410 b generates a resource issue as the VMs may be allocated multiple virtual cores, memory reservations and other resources, and also if VM is completely powered up the application in the VM may generate I/Os of its own changing the underlying VMDK 416 b which is not desired.

Referring to FIG. 4B, a replication system 400′ is the same as the replication system 400 except the replication system 400′ includes a shadow VM 430. The shadow VM is a shadow configuration of the target VM 410 b, which includes all the virtual disks of the virtual machine, with minimal CPU and memory configuration (e.g., 1 virtual central processing unit (CPU) with no CPU reservation and 64 MB or 256 MB of memory). The shadow VM 430 is configured to have the same ID as the target VM 410 b to make it transparent to virtual system management. The shadow VM 430 is also configured to load only up to a BIOS (basic input/output system) state only (i.e., the BIOS is the only process that is being performed), so that the target VMDK 416 b will be loaded to the kernel I/O stack but not accessed by the VM process, which conserves even less resources and also avoids alerts reported by the shadow VM 430 to management that it is unable to access its VMDK. For example, any VM that is powered up has OS running which accesses the internal disks and may change them, running the VM in BIOS mode only assures the no OS runs in the VM and the disks are not changed except from changes made by the splitter.

The shadow VM enables access to a target VMDK by multiple vDPAs without the target virtual machines fully running. This allows significantly higher (up to two orders of magnitude) performance than other tools while still keeping the consumption of virtual resources minimal. The access to the virtual disks of the shadow VM from the vDPA is done using a communications protocol. In order to write to the device the vDPA sends the data to the splitter which writes the I/Os to the VMDK. To read I/Os the vDPA sends a read request to the splitter. The splitter reads from the device and sends the response back to the vDPA.

Referring to FIG. 5, a process 500 is an example of a process to generate a shadow virtual machine (e.g., shadow VM 430). Process 500 powers down a target VM 410 b if powered up already (502). In some examples, the target VM 410 b may be powered up during a disaster recover test.

Process 500 removes VM 412 b from the inventory of the virtual machine hosts (504).

Process 500 configures shadow VM 430 (506), for example, by assigning an ID to the shadow VM 430 to be the same as the target VM 410 b and by attaching the same VMDKs (e.g., target VMDK 416 b) of the target VM 410 b to the shadow VM 430. Process 500 adds the shadow VM 430 to the inventory of the virtual machine hosts (512).

Process 500 powers up the shadow VM 430 to use limited resources (e.g., limited memory and CPU requirements) (514) and boots to the BIOS only (518) so that the VMDK will be loaded to the I/O stack but not accessed by the VM itself (i.e., the VM does not boot so the disk is accessible but the VM itself does not access it). Powering up the shadow VM 430 allows access to the target VMDK 416 b, by the splitter.

Referring to FIG. 6, a process 600 is an example of a process to write to the target VMDK 416 b after the target VMDK 416 b has been made accessible by the shadow VM 430. In one example, the process 600 is performed by the target splitter 414 b.

Process 600 polls the vDPA 408 b by issuing a read commands from splitter 414 b to vDPA 408 b (602) and receives metadata of the I/Os to replicate (608). Process 600 reads from the vDPA 408 b I/Os to be written (612) and writes the I/Os to the target VMDK 410 b (614).

Referring to FIG. 7, a process 700 is an example of a process to read from the target VMDK 416 b after the target VMDK 416 b has been made accessible by the shadow VM 430. Process 700 polls the vDPA 408 b by issuing one or more read commands from the splitter 414 b to the vDPA 408 b (702) and receives metadata of the I/Os to replicate (708). Process 700 has splitter 414 b reads data corresponding to the I/Os from the VMDK 416 b (712) and sends the data to the vDPA 408 b (714).

Referring to FIG. 8, one of the main limitations with virtual machines is that a virtual machine can only access a limited number of virtual devices (e.g., 60 VMDKs). In many cases the vDPA needs to access more than 60 journal devices. FIG. 8 describes a method to allow access to any number of journal devices.

A replication system 800 is the same as the replication system 400 except the replication system 800 includes a pseudo data storage system 820 and a kernel interface 824, both disposed at the virtual machine host 412 b, that allow access to multiple replica journals (e.g., a replica journal 818 a, a replica journal 818 b), which are VMDKs. The pseudo data storage system 820 acts as a dummy VMDK. That is, the vRPA does not see the replica journals 818 a, 818 but just the pseudo data storage system 820 i.e., there is a VMDK attached to virtual DPA as a disk and all interactions to the journals are done by sending I/Os to the pseudo data storage system 820. Interactions with the vDPA 408 b are handled by the pseudo data storage system 820. In one example, the kernel interface 824 is a splitter in a kernel.

In one example, the pseudo data storage system 820 is attached to the vDPA 408 b and is configured so that the kernel interface 824 will trap I/O received form the vDPA 408 b to the pseudo data storage system 820. The pseudo data storage system 820 will then act as a communication channel between the vDPA and the kernel. The kernel interface 824 can trap and respond to SCSI commands sent by the vRPA 408 b. The kernel interface 824 responds in a way that simulates a virtual storage system in the kernel. Therefore, in one particular example, the system (e.g., Linux) that the vRPA 408 b runs sees the single attached virtual device as a port connected to a complete storage system that can access multiple devices.

Referring to FIG. 9, a process 900 is an example of a process to access multiple replica journals. In one example, the process 900 is performed by the kernel interface 824. Process 900 discovers devices on a datastore (902). For example, the kernel interface 824 discovers the replica journals 818 a, 818 b (e.g., VMDKs) by scanning the datastore 420 b.

Process 900 receives an inquiry from the vDPA (906) and responds to the query (910). For example, the inquiry (e.g., a discovery) is received by the pseudo data storage system 820 to determine what the pseudo device is. The kernel interface 824 responds back to the vDPA 408 b using the pseudo data storage system 820. The response back notifies the vDPA 408 b that the pseudo data storage system 820 is a storage system though this is not true.

Process 900 receives a request from the vDPA 408 b for storage devices that are on the pseudo data storage system 820 (914). For example, the vDPA 408 b, being fooled in to determining that the pseudo data storage system 820 is actually a storage system, requests information on the storage devices on the pseudo data storage system 820.

Process 900 sends the discovered VMDKs (e.g., as determined in processing block 902) (918). For example, name, IDs and size of the VMDKs are returned.

Process 900 finishes discovery 920. In some examples, discovery of the VMDKs can be done by scanning the datastore (as described herein); using a naming convention for the VMDKs; using a directory structure and placing the VMDKs in specific directories (with or without a naming convention) and/or placing or communicating a table with the VMDK locations on the datastore. In some examples, completing the discovery process after the list of VMDKs is established includes (for each device) one or more of the follow: using a READ_CAPACITY command to get the device size. Using a STD_INQ command for general device information, using an INQUIRY command (e.g., pg 83) to get the device ID, using an INQUIRY command to other pages to get compatibility for features and extended command, thin/thick allocation and so forth; getting device geometry; and/or using other per device commands.

Process 900 receives an I/O (924) and send the I/O to the journal (928). For example, the I/O is sent from vDPA to the pseudo data storage system 820 and the kernel interface writes the I/O to the respective replica journal (e.g., replica journal 818 a or replica journal 818 b). For example, in the vDPA I/O stack located in the vDPA kernel there is code to trap commands to the pseudo data storage system 820 and to add LUN designation information to SCSI commands sent by the vDPA. This information is read by the kernel interface 824 (in virtual host kernel) and then stripped before the command is forwarded to the target LUN (replica journal). In one particular example, the information that is added is by using unutilized CDB (SCSI command description block—the meta data in the SCSI command) fields/bits to place the LUN number or adding an additional data block to the command scatter gather list for the information to be placed (each SCSI command has a scatter gather list containing the payload of the SCSI command, one option of sending the data includes increasing the SCSI command size (i.e. a SCSI command has a size of the payload in blocks we increase it by 1 and add one more block to the scatter gather list, the extra block includes the device of journal to be written to and the offset, then stripping the extra block and sending the data to the journal).

Referring to FIG. 10, in one example, a computer 1000 includes a processor 1002, a volatile memory 1004, a non-volatile memory 1006 (e.g., hard disk) and the user interface (UI) 1008 (e.g., a graphical user interface, a mouse, a keyboard, a display, touch screen and so forth). The non-volatile memory 1006 stores computer instructions 1012, an operating system 1016 and data 1018. In one example, the computer instructions 1012 are executed by the processor 1002 out of volatile memory 1004 to perform all or part of the processes described herein (e.g., processes 500, 600, 700 and 800).

The processes described herein (e.g., processes 500, 600, 700 and 900) are not limited to use with the hardware and software of FIG. 10; they may find applicability in any computing or processing environment and with any type of machine or set of machines that is capable of running a computer program. The processes described herein may be implemented in hardware, software, or a combination of the two. The processes described herein may be implemented in computer programs executed on programmable computers/machines that each includes a processor, a non-transitory machine-readable medium or other article of manufacture that is readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and one or more output devices. Program code may be applied to data entered using an input device to perform any of the processes described herein and to generate output information.

The system may be implemented, at least in part, via a computer program product, (e.g., in a non-transitory machine-readable storage medium such as, for example, a non-transitory computer-readable medium), for execution by, or to control the operation of, data processing apparatus (e.g., a programmable processor, a computer, or multiple computers). Each such program may be implemented in a high level procedural or object-oriented programming language to communicate with a computer system. However, the programs may be implemented in assembly or machine language. The language may be a compiled or an interpreted language and it may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program may be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. A computer program may be stored on a non-transitory machine-readable medium that is readable by a general or special purpose programmable computer for configuring and operating the computer when the non-transitory machine-readable medium is read by the computer to perform the processes described herein. For example, the processes described herein may also be implemented as a non-transitory machine-readable storage medium, configured with a computer program, where upon execution, instructions in the computer program cause the computer to operate in accordance with the processes. A non-transitory machine-readable medium may include but is not limited to a hard drive, compact disc, flash memory, non-volatile memory, volatile memory, magnetic diskette and so forth but does not include a transitory signal per se.

The processes described herein are not limited to the specific examples described. For example, the processes 500, 600, 700 and 900 are not limited to the specific processing order of FIGS. 5 to 7 and 9, respectively. Rather, any of the processing blocks of FIGS. 5 to 7 and 9 may be re-ordered, combined or removed, performed in parallel or in serial, as necessary, to achieve the results set forth above.

The processing blocks (for example, in the processes 500, 600, 700 and 900) associated with implementing the system may be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or part of the system may be implemented as, special purpose logic circuitry (e.g., an FPGA (field-programmable gate array) and/or an ASIC (application-specific integrated circuit)). All or part of the system may be implemented using electronic hardware circuitry that include electronic devices such as, for example, at least one of a processor, a memory, a programmable logic device or a logic gate.

Elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Various elements, which are described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims. 

What is claimed is:
 1. A method comprising: discovering devices on a data store comprising a first virtual device and a second virtual device; receiving an inquiry from a virtual data protection appliance; responding to the query by providing information on a pseudo data storage system; sending discovered devices to the virtual data protection appliance; receiving a first input/output (I/O) request at a kernel interface using the pseudo data storage system; writing the first I/O request to a first journal, used in a data replication process, in a first virtual device on the datastore; receiving a second I/O request at the kernel interface using the pseudo data storage system; and writing the second I/O request to a second virtual device on the datastore, wherein the second storage device is separate from the first storage device.
 2. The method of claim 1, further comprising attaching the pseudo data storage system to a virtual data protection appliance.
 3. The method of claim 1, wherein receiving a first I/O request at a kernel interface using the pseudo data storage system comprises: intercepting a command to the pseudo data storage system; and stripping designation information from the command before the command is forwarded to the pseudo data storage system.
 4. An apparatus, comprising: electronic hardware circuitry configured to: discover devices on a data store comprising a first virtual device and a second virtual device; receive an inquiry from a virtual data protection appliance; respond to the query by providing information on a pseudo data storage system; send discovered devices to the virtual data protection appliance; receive a first input/output (I/O) request at a kernel interface using the pseudo data storage system; write the first I/O request to a first journal, used in a data replication process, in a first virtual device on the datastore; receive a second I/O request at the kernel interface using the pseudo data storage system; and write the second I/O request to a second virtual device on the datastore, wherein the second storage device is separate from the first storage device.
 5. The apparatus of claim 4, wherein the electronic hardware circuitry comprises at least one of a processor, a memory, a programmable logic device or a logic gate.
 6. The apparatus of claim 4, further comprising circuitry to attach the pseudo data storage device to a virtual data protection appliance.
 7. The apparatus of claim 4, wherein the circuitry to receive a first I/O at a kernel interface using a pseudo data storage system comprises circuitry to: intercept a command to the pseudo data storage system; and strip designation information from the command before the command is forwarded to the pseudo data storage system.
 8. An article comprising: a non-transitory computer-readable medium that stores computer-executable instructions, the instructions causing a machine to: discover devices on a data store comprising a first virtual device and a second virtual device; receive an inquiry from a virtual data protection appliance; respond to the query by providing information on a pseudo data storage system; send discovered devices to the virtual data protection appliance; receive a first input/output (I/O) request at a kernel interface using the pseudo data storage system; write the first I/O request to a first journal, used in a data replication process, in a first virtual device on the datastore; receive a second I/O request at the kernel interface using the pseudo data storage system; and write the second I/O request to a second virtual device on the datastore, wherein the second storage device is separate from the first storage device.
 9. The article of claim 8, further comprising instructions causing the machine to attach the pseudo data storage device to a virtual data protection appliance.
 10. The article of claim 8, wherein the instructions causing the machine to receive a first I/O at a kernel interface using a pseudo data storage system comprises instructions causing the machine to: intercept a command to the pseudo data storage system; and strip designation information from the command before the command is forwarded to the pseudo data storage system. 